The present invention relates to active compound concentrates having herbicidal action, comprising    a) at least one 4-benzoyl-substituted pyrazole compound of the formula I            in which        
                R1, R3 independently of one another are hydrogen, halogen, methyl, halomethyl, methoxy, halomethoxy, methylthio, methylsulfinyl or methylsulfonyl;        R2 is a 5-membered heterocyclic radical which is unsubstituted or carries 1, 2, 3 or 4 substituents selected from the group consisting of halogen, C1-C6-alkyl, C1-C4-alkoxy, C1-C4-haloalkyl, C1-C4-haloalkoxy and C1-C4-alkylthio;        R4 is hydrogen, halogen or methyl;        R5 is C1-C6-alkyl, C3-C6-cycloalkyl or C3-C6-cycloalkylmethyl; and        R6 is hydrogen or C1-C4-alkyl;        or one of its agriculturally useful salts, and            b) 2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)acetamide (dimethenamid).
The invention also relates to the use of such active compound concentrates for controlling unwanted vegetation, in particular for controlling graminaceous harmful plants.
Pure crops of agriculturally interesting useful plants are required for efficient and profitable practice of industrialized agriculture and for ensuring a consistent product quality. The selective sensitivity of different plant groups with respect to certain metabolic inhibitors or other cell toxins may be utilized for the targeted control of unwanted foreign vegetation (growth of harmful plants) on the areas under agricultural cultivation. Here, it is desirable in principle to enhance both the absolute efficacy and the specificity of the active compounds used (herbicides) against harmful plants.
The specificity and, within certain limits, the absolute efficacy can be enhanced by using combinations of a plurality of specific active compounds which attack at different points of the metabolism of the target plants. If the activity of the combination exceeds the sum of the individual activities significantly, this is referred to as synergism (occasionally also as superadditive effects).
The herbicidal action of the 4-benzoyl-substituted pyrazole compounds of the formula I is known from WO 96/26206 and WO 98/31681.
The herbicidal action of 2-chloro-N-(2,4-dimethyl-3-thienyl-N-(2-methoxy-1-methyl-ethyl)acetamide, also referred to as dimethenamid, is known from GB 2,114,566. Owing to the presence of two chiral elements (the chiral axis along the bond between the 3-position of the thiophene ring and the nitrogen atom of the amide group, and a center of asymmetry at carbon 1 of the 2-methoxy-1-methylethyl group), dimethenamid is a mixture of four stereoisomers. The stereoisomers of dimethenamid which, with respect to the asymmetric carbon atom of the 2-methoxy-1-methylethyl group, have the S-configuration are also referred to as S-isomer or as dimethenamid-P.
It is known from WO 99/65314 that the joint application of 4-benzoyl-substituted pyrazole compounds of the formula I and dimethenamid results in a herbicidal action which is increased compared to the application of the individual compounds. Formulations comprising both active compounds are not described in this publication.
What is desired, not least for reasons of practicability, are formulations comprising both the 4-benzoyl-substituted pyrazole compound of the formula I and dimethenamid in relatively concentrated form. Here, a number of problems have to be solved, in particular if the formulation comprises the active compounds in concentrated form. Since, prior to their application, such active compound concentrates are usually diluted with water, it has to be ensured that the concentrates can be diluted with water without any problems, and that the resulting aqueous dilution comprises the active compounds in relatively uniformly distributed form. However, frequently, especially concentrated active compound formulations (active compound concentrates) have, on prolonged storage, a tendency to undergo phase separation and/or to precipitate solids. On dilution with water, this then results in an uneven distribution of the active compounds in the aqueous dilution and/or inaccuracies when metering out the active compounds, which frequently eliminates the desired superadditive effect.